The present invention relates to a semiconductor laser driving circuit which can be used in an optical disk apparatus, a laser beam printer, a copying machine, an optical data communication system, various measuring device, or the like, an optical disk apparatus and an image recording apparatus using the semiconductor laser driving circuit.
A semiconductor laser has many features: easy modulation of light-emission power by control of the driving current, a compact structure, small consumption power, and high electro-photo conversion efficiency. For this reason, the semiconductor laser is popularly used in an optical disk apparatus and an image recording apparatus such as a laser printer, a copying machine, or the like.
However, the semiconductor laser has the following characteristics:
(1) The differential quantum efficiency changes due to changes in temperature and aging. PA0 (2) The threshold value of the laser driving current changes due to changes in temperature and reflected light. PA0 (3) Mode hopping noise is generated due to reflected light.
The amount of light emitted by the semiconductor laser varies due to these characteristics. In view of this problem, a circuit for controlling to maintain a constant amount of light by monitoring the amount of output light from the semiconductor laser is used. For example, a conventional control circuit disclosed in Japanese Patent Laid-Open No. 4-208581 is known. In this circuit, light output from a semiconductor laser is received by a photodetector serving as a light-receiving element to be converted into a light-receiving current proportional to the light emission amount, and the light-receiving current is negatively fed back to detect any error from a light-emission power command signal using an error detection circuit. Then, the driving current of the semiconductor laser is controlled so that the error is assumed to be zero. In addition to such feedback control system, the control circuit also comprises a compensation circuit for negatively feeding back a compensation current to the input of the error detection circuit so as to compensate for a phase lag of the feedback control loop.
An image recording apparatus such as a laser printer is required to have a high extinction ratio indicating the ON/OFF ratio of light. However, the feedback efficiency considerably lowers and control can hardly be made in the OFF region of the semiconductor laser, i.e., in the neighborhood of the threshold value or less upon oscillation of the laser. For this reason, the conventional semiconductor laser device suffers a decrease in extinction ratio and a light-emission delay.